Non-linear radar (NLR) systems are known. NLR systems use two or more collimated, millimeter wave beams having frequencies that are separated by a difference frequency (Δf). The difference frequency is usually, although not always, located in the microwave (centimeter wave) range of the electromagnetic spectrum.
Such collimated beams interact when they are brought together. For example, the collimated beams can be brought together at a distant target. Non-linear electrical components such as diodes, transistors, integrated circuits, and detectors, as well as surfaces or structures that have non-linear electrical characteristics (such as due to corrosion, rust, or oxidation) facilitate interaction of the two beams. This interaction causes the production of a difference frequency and harmonics thereof.
By choosing the appropriate Δf value or values, it is possible to interact with electronic circuits associated with the target. Such interaction can, for example, interfere with the normal operation of the electronic circuits.
The interaction can occur in various degrees. For example, a mild interaction can cause temporary interference with certain selected functions of the target. More violent interaction can result in the permanent destruction of the target or of its key components or systems.
Most commonly, the level of interaction with the target is determined by the power density delivered to the target. The level of interaction is also determined by how effectively target resonances can be taken advantage of at the target. There is a wide variety of different types of resonances, from electrical resonances created by circuit components, e.g., lumped circuit elements, to electromagnetic resonances produced at microwave frequencies by such structures as cavities, boxes, and instrument cases.
The difference frequency Δf can be re-radiated by the target. This re-radiated radio frequency energy can define a radar return that can be used to determine the presence of a device and/or determine the location thereof.